The present invention relates to mechanisms for maintenance of mainlines, and more particularly to machines for cleaning outer surfaces of pipes of a mainline by removal old bitumen coating and dirt.
It is known that anticorrosive coating of operating pipelines degrades with time under the action of environmental factors (temperature difference, mechanical damages and the like). Pipe metal corrodes in the zones of degradation of anticorrosive coating so that even perforations of the pipe walls may occur, especially at the transversal welds of the pipeline due to unlike structure of the weld metal and the parent metal of the pipe, which is still more pronounced for underground pipelines under permanent action of soil electrolyte.
It will be apparent from the above that the repair of anticorrosive coating of the outer surface of a mainline should be done timely, especially because of the fact that the service life of anticorrosive coating is much shorter than that of the metal pipes.
It has been so far the world-wide practice to repair mainlines by replacing portions thereof by new ones. This is associated with temporary suspension of supply of a product being transported thus reducing the throughput capacity of the pipeline as a whole. Therefore, there is a long-felt need to resolve the problem of overhaul of anticorrosive coating of the outer surface of pipes in a mainline without interruption of supply of a product along the pipeline during the repair.
For that purpose there are provided machines for cleaning the outer surface of pipes of a mainline.
The invention may be most advantageously used for repair of operating mainlines of large diameter, in particular, oil and gas pipelines.
Known in the art are machines for cleaning outer surface of pipes of a mainline comprising a self-propelled carriage which is moved over the surface of a pipe being cleaned axially thereof during cleaning, and a working member mounted on the frame of the carriage which has a hollow annular casing accommodating an annular rotor coaxial with the pipe being cleaned which supports working tools.
Both casing and rotor of such machines are made detachable each consisting of two half-rings, one half-ring of the casing being the top half-ring rigidly fixed to the frame of the self-propelled carriage, and the other casing half-ring is the bottom half-ring.
In order to mount the machine on the operating pipeline, the bottom half-ring of the casing is first detached, then the rotor is withdrawn and dismantled into two half-rings. Subsequently the self-propelled carriage is installed with the top half-ring of the casing astride the pipeline, and the rotor is mounted on the pipeline then the rotor is aligned with the top half-ring of the casing, whereafter the bottom half-ring is mounted near the top half-ring, and their mating planes are attached to one another.
The machine is dismantled in the reverse order.
During repair of an underground pipeline, a trench is first excavated, then the pipeline is lifted at a height sufficient for the passage of the working member of the machine. The same result may be achieved by undermining the lower portion of the pipeline.
The main disadvantage of prior art machines for cleaning the outer surface of pipes consists in that the above-described operations of mounting and dismantling of the machine are require much time in view of a large number of labour-consuming steps involved so that the operation of the machine is unproductive and also unsafe for the operating staff.
In addition, heavy weight of detachable parts of the casing and rotor of the working member of the machine requires the employment of lifting gears which is very inconvenient, especially in trenches.